Antenna system



' April 29, 1947.

T. H. CLARK ANTENNA sYs TEM Filed "March 5, 1943 4 Sheets-Sheet 1 ATTORAEY April 29, 1947. T. H. CLARK 2,419,538

' ANTENNA SYSTEM Filed March 5, 1945 4 Sheets-Sheet 2 IN VEN TOR. 795 vol? H. c4 HIP/f ATTORAEY T. H. CLARK ANTENNA SYSTEM April 29, 1947.

Filed March 5, 1943 4 Sheets-Sheet 3 INVENTOR. TEE V01? CZfl/FK A T TOME) T. H. CLARK ANTENNA SYSTEM April 29, 1947.

Filed March 5, 1945 4 Sheets-Sheet 4 IN V EN TOR. 7' PE V01? h. CL ARK ATTO Patented Apr. 29, 1947 UNITED STATES ANTENNA SYSTEM Trevor H. Clark, New York, N. Y., assignor to Federal Telephone and Radio Corporation, Newark, N. J a corporation of Delaware Application March 5, 1943, Serial No. 478,081

16 Claims. 1

This invention relates to improvements in antenna systems, and more particularly to a short wave crossed loop wave collector adapted for use for installation on board ships, especially on top of masts.

An object of this invention is to provide a novel improved antenna assembly including crossed loops, sense antenna and counterpoise, which is especially adapted for use in connection with direction finding systems aboard ships.

Another object of this invention is to provide an antenna assembly of the type described which can readily be mounted upon the usual ship mast structures.

A further object of this invention is the provision of an antenna assembly including crossed loops, sense antenna and counterpoise, in which the stray capacity between the crossed loops and the counterpoise is reduced to a minimum.

An additional object of this invention is directed to providing an antenna assembly including crossed loops, sense antenna and counterpoise in which the sense antenna and counterpoise are interconnected by a shielded dummy 100p network immediately adjacent thereto.

Still another object of this inventio'n-isdirected to a novel sense antenna-counterpoise circuit which assures 180 phase displacement between them and maximum coupling to a dummy loop network.

A still further object of this invention is the provision of an antenna assembly for direction finding systems on board ship in which the capacity effect of the mast uponwhich the antenna system is mounted is appreciably reduced.

An additional object of this inventionis directed to a novel antenna assembly for direction finding purposes including a crossed loop; sense antenna and counterpoise, in which the counter- I poise is positioned above the loop directly between it and the sense antenna.

With these and incidental suggestions in view, the invention consists in certain features of construction and combination of parts which are set forth in the appended claims, and a preferred form of embodiment whereof is hereinafter described with reference to the drawings which accompany and form part of the specification,

' 2 Fig. 5 is a top view of the dummy loop shield included in Fig. 3.

The general antenna assembly according to my invention will be readily apparent from a 5 study of Figs. 1 and 2. Primarily it includes a generally vertical supporting rod II) from the mid-point of which extend four radial arms l2 spaced 90 relatively to one another and attached to the rod It by means of a suitable connector l3. The bottom of the supporting rod I0 is held in a strengthening support 14 which, in turn, is mounted upon a generally hemispherical base member IS. The latter, in turn, may be attached to the top of a ship mast indicated at I]. The

four arms I: may be interconnected by bracing bars attached thereto by suitable clamping devices 22.

The crossed loop in accordance with the present invention, is formed by two flexible shielded 0 cables 2'4 and 26, the apices of which pass through a top mount 18, attached to the top of the supporting rod I0, the ends of which are fastened within the base member 16, and the central portions of which are held by fastening devices 28 on the ends of the respective arms l2. Above the top mount I8 is fixed an insulating ring 29 which supports a metal cap 30 from which projects a plurality of counterpoise rods 32. These rods are positioned at 90 relatively to one another and, according to one feature of the present invention they extend in a direction to bisect the angle between the crossed loops or, in other words, each counterpoise rod is at an angle at to the loops immediately beneath and to either side of it. A sense antenna 34 extends vertically upwardly from an insulating disk 36 mounted on top of the cap 30.

By reason of the general arrangement just described it has been found that the capacity between the counterpoise and the crossed loop antenna is, materially reduced by having the counterpoise rods extending at an angle bisecting the angle between the loops. By placing the counterpoise above the crossed loops, the capacity he- 45 tween the counterpoise and the mast is also reduced while, additionally, the juxtaposition of the sense antenna and counterpoise by reason of the described arrangement permits them to be directly interconnected, as by a dummy loop network without the interposition of a long transmission line.

The upper portion of the antenna system, and more particularly the top mount l8 and the cap 30 together with associated parts is more fully illustrated in Fig. 3. It will be seen that the top of the supporting rod I0 is provided with a flange 38, while the lower portion of the top mount I8 is provided with a comparable flange 40, which permits an easy assembly of the top mount upon the rod as by bolts 42. The insu1at- 3 ing ring 29 is likewise attached to the top of the top mount it by means such as bolts 54 while the cap Bilis mounted upon the ring 29 by similar means such as bolts to. The insulating disk 36 may be attached to cover the cap as by screws 23.

As previously described, the cap 39 serves-to support the counterpoise rods 32 and, at the same time electrically connects one with the other. For this purpose the inner ends of the counterpoise rods are formed with stifiener sections 55 which may be provided with threaded extensions 52 projecting through openings in the cap as and secured thereto by nuts The bottom of the sense antenna 3 3 is similarly provided with a stiffening section 53 having a threaded projection 58 extending through a central opening in the insulating disk 35 and attached there to by nut so.

The tops of the cables forming the two loops pass, as previously described, through the top mount l8. In order to securely hold the loops in place and prevent a strain upon the top, curved portions, the loops are securely held in openings in this top mount. For this purpose the openings in the top mount it may be provided with a Bakelite or other insulating bushing 62 through which is passed a metal sleeve 66 which, in turn, encloses a rubber sleeve (36 immediately surrounding and adapted to be pressed against the cable 24. The sleeve 65 is formed with a collar 8% on one end which presses against the inner end of the bushing 62, limiting movement of the sleeve 68 in the downward direction, and is threaded on its outer end. A cap 7'5 screws over the threaded'end or" the sleeve 65 and, through a metal washer I l presses tightly against the rubber sleeve 6 squeezing it down the surface of the cable. In accordance with the present invention each loop is preferably formed from a flexible shielded cable, the shield being formed by an outer steel braid it, plus an inner copper braid. This shielding braid is cut off just above the collar '68 and a ferrule 12', soldered to the braid,-this ferrule projecting over the end of the collar 68 and assisting in preventing downward strain upon the cable. As is common practice in shielded loop construction the upper portion of each loop will be unshielded so that by removal of the braid iii, and any inner braid, if used, the top of each loop will consist solely of insulated conductor 78. In Fig. 3 there may also be seen the end of the cable 26 which may pass over (or beneath) the unshielded portion 18 of the cable i i. The cross-section of the unshielded cable 26 is indicated at it. In order to properly attach the cable holding means in the top mount l8, and to generally make connections within this top mount, the latter may be in a somewhat skeletonized form being provided with a plurality of through working apertures il As previously mentioned, one of the advantages of the present construction lies in providing a short interconnection through a dummy loop between the sense antenna and counterpoise. Fig. 3 also shows the manner in which such a dummy loop assembly may be mounted with the top mount is. This dummy loop network is preferably mounted within a shielding can 80, the network itself which may be of conventional form being diagrammatically indicated at 82. The can 853 is attached to a flanged cylindrical member with a water-proof gasket 86 therebetween, as by means of screws 88. The cylindical member 86 is internally threaded at its other end to receive a compression nut 95 which squeezes a compression gland 95 between washers 94 and 98. Above the washer 95 is positioned a split sleeve We which supports a jack plug H32 against the gasket 86. A second gasket I04 spaces the jack plug Hi2 from the gasket 86. The jack plug H32, in turn, has connected thereto as by threaded extensions I96, the banana plugs H33 which extend upwardly into the can 8!] for connection with the dummy loop network 82. The two lines from the dual cable 92 are respectively attached to the lower ends of the banana plugs, the cable 92 thus acting as a transmission line from the dummy loop network down through the center of the hollow supporting rod ill to the base member It.

The lead-ins to the dummy loop through the shielding can it are brought to insulators H0 and H2, these lead-ins being respectively indicated at H4 and H6. The lead-in H6 may be interconnected with the sense antenna through the lead wire HB connected to a tab I20 positioned beneath the nut 69. The lead-in to the counterpoise may be effected by the lead wire, l22 connected to a tab 124 beneath the nut-54. Since the cap 38 to which all of the counterpoise rods are attached is conductive metal, the one lead wire-I22 is sufficient for, this purpose. As illustrated in Fig. 3 and with more particularity in Fig. 5 the'dummy loopshield can 80 may also support part of a lightningarrester gap. On top of the .shield can 80 is mounted, as by welding, a plate 36 frornwhich projects upwardly a pointed rod L26 which, in turn is spaced from a downwardly extending rod I28 which may also be attached to an extension on the tab I20. Since the shield can 1-80 isgrounded to-the mast throughthe screws 88,,this arrangement serves inherently as a lightning arrester gap for the sense antenna 34. I a

One feature of the present invention lies in proper proportioning of the primary circuit of the dummy loop network 82. This circuit is so balanced that the resonant frequency as determined by the capacity of sense antenna .to the counterpoise, the shielded loop andthe mast, the capacityof the counterpoise to the shielded loop and the mast, the internal capacity of the primary winding of the transformer 200, the capacity of this winding relatively to the Faraday shield 202 and the inductance of the primary winding,

will be greater. than the operating frequency of the loop. By means of, thisfproportioning, a phase displacement of exactly between the sense antenna and the counterpoise can be obtained, and greater coupling. to the dummy loop network results despite a decrease in the number of windings on the transformer. Adjustment, of this primary circuit may be effected, if necessary, for optimum results by adjusting the length of the-sense antenna or by providing a suitable capacitor (not shown) between the primary circuit and the Faraday shield. v a

For the purpose of properly proportioning the sense antenna to the counterpoise in their-resonant circuit, such sense antenna may be-formed as of an adjustable length in the manner more clearly indicated in Fig. 4.- As there illustrated the counterpoise rod 34 itself is formedas ahollow tube slidable within a rod support 43!]. The latter may be shrunk at one end within alongitudinal bore of the, rod stiffener 56, while its outer end may be split and externally threaded to receive a surrounding nut I32. When the nut I32 is tightened it will squeeze the rod supportabout the rod 32, thus, holding the same in place. When the nut I32 is loosened, the rod 32 may be longitudinally adjusted as desired. The hollow rod 32 will be provided with a plug I34 in its end, which may be pressed into the end of the rod.

While it has not been specifically illustrated in,.

detail, the counterpoise rods 32 may be formed adjustably in a manner identical with that just described in connection with the sense antenna rod 34. It is pointed out, furthermore, that adjustable rods such as have just-been described various elements forming this antenna system in some detail, it will be obvious to those skilled in this art that various changes in details of construction may be effected without departing from the spirit of my invention. Accordingly, while I have described the principles of my invention in connection with certain specific apparatus, it is to be clearly understood that this description is .made only by way of example and not as a limitation on the scope of my invention as set forth in the objects and the accompanying claims.

I claim:

1. An antenna system comprising, in combination, a shielded loop antenna comprising a pair of loops having a common axis and positioned at 90 relatively to one another, means for shielding said loop antenna, a vertical sense antenna extending upwardly abovesaid loop antenna along the axis thereof, a counterpoise consisting of four radially directed rods mounted at 90 relatively to one another, and means for mounting said counterpoise coaxially with and above said loops, and below said sense antenna.

2. The combination according to claim 1, in combination with a dummy'loop network, and circuit means interconnecting said sense antenna with said counterpoise, said circuit means including a transformer whose primary winding has such a number of turns it forms together with .said sense antenna and counterpoise a resonant circuit whose resonant frequency is higher than that of said shielded loop".

3. The combination according to claim 1, in 'which the rods forming the counterpoise bisect the angles between the loops.

4. A wave collector including, in combination a hollow base member, a hollow supporting rod positioned on and communicating with said hol- 'low base member, a hollow top mount, open at opposite vertical ends, supported on and com- :municating with the top of said supporting rod, .four arms positioned at right angles to one another, extending radially outwardly from sub- ;stantially the vertical mid-point of said support- :ing rod, a loop antenna comprising two loops, each loop having its top fixed to said top mount and its ends fixed in said base member, one loop being supported by two opposite arms and the other loop being supported by the other two opposite arms, whereby the two loops are positioned at 90 relatively to one another, means for shielding each loop, a cap mounted on said top mount, a vertical sense antenna supported :from said cap, a counterpoise attached to said cap, said counterpoise comprising four radially directed rods extending from said cap at right angles to one another, and transmission line means leading from said sense antenna and counterpoise through said hollow supporting rod to said base member.

5. The combination according to claim 4, in which each'of said loops and the shielding means therefor is formed of shielded insulated flexible cable, in combination with means for insulating said shielded cable from said top mount.

6. The combination according to claim 4, in which each of said loops and the shielding means therefor is formed of shielded insulated flexible cable, and the shielding is removed from that portion of the loop within said top mount, in combination with means for insulating said shielded cable from said top mount.

7. The combination according to claim 4, in combination with means for insulating said cap from said top mount, and means for insulating said sense antenna from said cap.

8. The combination according to claim 4, in which said transmission line includes a dummy loop transformer network interconnecting said sense antenna and counterpoise and a dual cable leading from said network to said base, in combination with a hollow container enclosing said network, means for mounting said container inside of said top mount, and means for mechanically supporting said dual cable from said container. I

9. The combination according to claim 4, in which the rods forming the counterpoise bisect the angles between the loops.

10. A wave collector including in combination a hollow base member, a hollow supporting rod positioned on and communicating with said hollow base member, a hollow top mount open at opposite vertical ends, supported on and communicating with the top of said supporting rod, four arms positioned at right angles to one another, extending radially outwardly from substantially the vertical mid-point of said supporting rod, a loop antenna comprising two loops, each loop having its top passing through said top mount and its ends fixed in said base member, one loop being supported by two opposite arms and the other loop being supported by the other two opposite arms, whereby the two loops are positioned at relatively to one another, means for shielding each loop, an insulating ring fastened on said top mount, a metal cap attached to said insulating ring, an insulating disk covering said metal cap, a vertical sense antenna provided with a through bolt extending through said insulating disk, a counterpoise attached to said metal cap, said counterpoise comprising four radially directed rods extending from said cap at right angles to one another, a hollow metal container mounted within said top mount" and grounded to said supporting rod, a dummy loop transformer network positioned within said container, means for interconnecting said dummy loop transformer network with said sense antenna and counterpoise, a dual cable leading from said dummy loop transformer network to said hollow base, a downwardly extending rod electrically connected with said'sense antenna, and an upwardly extending rod attached to said metal container, the upper end of said rod being spaced below said downwardly extending rod to form with the latter a lightning arrester gap.

11. The combination according to claim 10, in which the rods forming the counterpoise bisect the angles between the loops.

"12. 'fhe ombination aepr'ding to claim '10, in which each of "said loopsandtlie 's'hieldingfineans therefor is formed of ashielded, insulated 'flexible cable, in combination "with means 'f'orinsulating said shielded cable iror'n said topmount.

13. The combination aco'o'rdin g t'o claim 10, in which each of said loops and the shielding means therefor'is formed of 'ashielded, insulated 'fl'exible'oable, and in which the shielding isrenioved from that'portion'of thec'ab'le'within "s'aidtop mount, in combination with nieansf'or insulating said shielded ca5le from said topmount.

14. The combination according to -claim 4,in combination with a dummy loop 'ntworkj'and circuit means interconnecting 'sai'd sense "antenna With'said counterpoise, said circuit means including a transformer whose primary Win'dihghas such a number of turns it forms together with said sense antenna and counterpoise a'res'onant circuit whose resonant frequency is higher than that of said shielded loop.

15. An antenna system comprising in combination a loop antenna comprising a'pair of loops haVing 'apOnimOn axis and positioned substantially at 'rightfangles to-one another, means for shielding-said loop antenna,ta-vertica l sense'antenna extendingu'pwardly above said loop an tenna along the aXisthereof, a count'erpoise'com- *prisin'g'conductive means substantially symmetrically disposed with respect to vsaid sense antenna and. means for mounting said counterpoise eo- 'shielding'said loop' antenna,- a vertical sense aning said counterpoise coaxially with and above said loops "and below saidgs enseantenna,

TREVOR H5 CLARK. 

